The present invention is directed to bin level indicators, and more particularly to an improved apparatus of the rotating-paddle type for indicating the level of flowable material in a storage tank or bin.
Bin level indicators of the above-noted type typically comprise a motor carried for limited rotation within a protective enclosure and connected to a rotatable paddle that is adapted to engage flowable material within a storage bin when the material rises to the bin level at which the rotating paddle is disposed. Material drag on the paddle causes the motor drive torque to rotate the motor rather than the paddle, which rotation is sensed by one or more switches carried within the enclosure. The switches may be connected to deactivate a conveyor feeding material to the bin, to remove power from the indicator motor and/or to perform other control functions related to material level. Examples of bin level indicators of the described type are shown in the Grostick U.S. Pat. No. 2,851,553, Gruber U.S. Pat. No. 3,542,982, Fleckenstein U.S. Pat. No. 4,095,064, Levine U.S. Pat. No. 4,147,906, Roach U.S. Pat. 4,392,032 and Fleckenstein et al U.S. Pat. No. 4,695,685.
A problem is encountered in application of conventional apparatus to lightweight (low density) materials such as fly ash and plastic powder or pellets. Specifically, light material weight is sometimes insufficient to retard rotation of the paddle permitting the paddle to "plow" a path through the material and continue rotation even though covered by material. Another and related problem lies in factory setting of spring force on the motor, which must be overcome by drag on the paddle to permit rotation of the motor against the spring when drag is placed on the paddle, and to return the motor to the normal position when the paddle is again free to rotate. Typically, spring force is determined during apparatus design as a function of a typical material weight and drag, and is not adjustable in the field as a function of density of material in connection with which the indicator will be used.
Another problem typically encountered with conventional bin level indicators of the subject type involves inability of an observer or operator to determine the condition of the indicator, and consequently level of material within the bin with respect to the indicator, through observation of the indicator itself. An indicator may be positioned at the top of a tall storage bin, for example, and connected to a remote display panel for indicating material level at a central location. However, an observer at the bin itself cannot determine the status of the bin level indicator. A further problem is encountered in connection with bin level indicators of the subject type in which power is removed from the indicator motor when rotation of the paddle is retarded. Insufficient power is dissipated within the indicator housing to generate heat sufficient to prevent condensation during cold weather, which can damage switch contacts and other components of the indicator.